title: High-resolution microcoil NMR for analysis of mass-limited, nanoliter samples.
abstract: An improved nanoliter-volume NMR probe design places the microcoil and capillary at the magic angle (57.7 degrees) with respect to the external magnetic field. Using an NMR probe which requires a total sample volume of just 200 nL, high-resolution 300-MHz 1H-NMR spectra (line width, 0.6 Hz) are presented of 10 mM alpha-bag cell peptide for an observe quantity of 45 ng (50 pmol in 5 nL). For the volume of sample inside the microcoil (the observe volume, Vobs), the 3 sigma limit of detection (LOD) is 9 ng (10 pmol, 2mM) for data obtained in 15 h. To reduce the data acquisition time, a probe with a greater Vobs is developed. As an example of a rapid, mass-limited analysis, a concentration corresponding to 400 ng of menthol dissolved in Vobs = 31 nL (82.6 mM) yields a spectrum in 9 min (LOD = 6.9 ng, 44 pmol, 1.4 mM). To illustrate improvements in concentration sensitivity, a spectrum is acquired in 45 min for 400 ng of menthol dissolved in a total sample volume of 200 nL (12.8 mM). Compared to a commercial nanoprobe for the same mass of menthol, these two examples reduce data acquisition time by at least 95%. Both model compounds demonstrate substantially improved concentration LODs compared to those obtained in previous high-resolution, microcoil NMR work. These advances illustrate the utility of enhanced sensitivity provided by NMR microcoils applied to nanoliter volumes of mass-limited samples.
authors.affiliation: Beckman Institute, University of Illinois, Urbana 61801, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Olson
authors.forename: M E
authors.initials: ME
authors.lastname: Lacey
authors.forename: J V
authors.initials: JV
authors.lastname: Sweedler
mesh_terms: D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation* / Q000379:methods; D008610:Menthol / Q000032:analysis; D010455:Peptides / Q000032:analysis
chemical_list: D007202:Indicators and Reagents; D010455:Peptides; D008610:Menthol